1. Field
Disclosed embodiments related to an intake valve of an internal combustion engine.
2. Related Art
In a high-rotation and high-powered engine mounted in a motorcycle etc., it is required for moving parts of a valve train mechanism to reduce weights, and accordingly, intake and exhaust valve which are made of titanium alloy have been become usable.
The intake and exhaust valves made of titanium alloy have high specific strength and are suitable for weight saving, but have inferior abrasion resistance. Thus, it is necessary for a stem end portion of the valve to perform an expensive surface treatment such as fine shot peening and surface coating (for example, DLC (diamond-like carbon)). Since the titanium alloy is also expensive, manufacturing cost of these valves is increased.
Patent Document 1 (Japanese Utility Model Laid-Open No. 61-202606) discloses intake and exhaust valves including a valve body and a valve stem made of titanium alloy, and a stem end portion connected to dissimilar metal (for example, iron metal) having excellent abrasion resistance.
In the intake and exhaust valves disclosed in Patent Document 1, portions other than the stem end portion are made of titanium alloy. Thus, they can reduce their weight, but their cost is increased.
Furthermore, although the durability of the stem end portion is improved due to the dissimilar metal (iron metal), the reliability at a portion connecting the dissimilar metal and the titanium alloy is not necessarily sufficient.